FIG. 3 is a constitutional drawing of a conventional laser generator. In the laser generator, power supply 32 excites laser medium 31. Translucent mirror (hereinafter, called mirror) 34 and laser light amplifying mirror (hereinafter, mirror) 35 oscillate a caused light to be generated as laser beam 36. Mirror holder 33A and 33B hold mirrors 34 and 35, respectively. Mirror 34 is a translucent mirror allowing the laser beam to be output to outside. Mirror 34 is generally called an output mirror.
Laser beam 36 which is amplified by mirrors 34 and 35 and output through mirror 34 to outside passes through inside laser introducing duct (hereinafter, duct) 37 that protects the laser beam, shutter unit (hereinafter, shutter) 38, and light path duct 39 in this order. Then the light is reflected by reflecting mirror 40 and refracted by condensing lens (hereinafter, lens) 41 to be utilized as a beam for laser processing.
Shutter 38 is composed of reflect mirror 38A, actuator 38B driving reflect mirror 38A, and absorber 38C absorbing the laser light reflected by reflect mirror 38A. When laser beam 36 is not taken outside, actuator 38B drives reflect mirror 38A into a path of the laser light reflecting the light so as absorber 38C absorbs the laser beam reflected by reflect mirror 38A.
It is difficult to seal airtight components disposed outside mirror 34, i.e., duct 37, shutter 38 and light path duct 39 due to its structure. Consequently outside air containing oil, dust, iron powder and other impurities can flow into the components. If the air containing such impurities flows into the light path of the components and attaches to surfaces of the mirrors and lens 41, the laser light may burn the surfaces, which causes lowering power of the generator and damaging the optical components seriously.
In order to prevent such incidence, Japanese Patent Unexamined Publication Nos. S61-286085 and H3-60890 disclose a technology of sending filtered air or nitrogen gas into a vicinity of the optical components of the generator. That is, the conventional laser generator includes gas supply source 42 supplying air, filters 43A and 43B, and gas introducing parts 44A and 44B which are air exhaust nozzles. Filters 43A and 43B filter the air supplied by gas supply source 42, producing clean air. Gas introducing parts 44A and 44B send the clean air into a vicinity of mirror 34 and lens 41 and clean up air in the vicinity of the optical components. Instead of air, gas supply source 42 can supply nitrogen gas using a commercially available nitrogen cylinder that contains fewer impurities.
The air or the nitrogen gas that purges impurities at the vicinity of the mirror 34 and lens 41 includes far less impurities than ordinary air does. However in the ordinary method where gas introducing parts 44A and 44B forcefully blow out impurities, the blow out air is so called a turbulent flow having inconsistency in velocity and direction in the stream. Because of the reason, an eddy flow tends to occur inside duct 37 and inside light path duct 39 near lens 41, inefficiently expelling out contaminated air already existing in duct 37 and light path duct 39, therefore impurities concentration on the surface of the mirrors and lens 41 is not thoroughly reduced.
The effect of air flow that purges impurities (air purge effect) on the surface of mirror 34 can be examined by measuring oxygen concentration near the surface of mirror 34 by using nitrogen gas instead of air. It may be supposed that oxygen concentration on the surface of mirror 34 is reduced as the nitrogen flow increases, but actually the oxygen concentration does not fall down below a certain level. Even when nitrogen flow is increased for reducing the oxygen concentration below 100 ppm, the concentration is not in fact reduced lower than 0.2% (20,000 ppm) as long as the conventional air blowing method is employed. Thus, the method does not sufficiently protect components i.e. the mirrors and the lens that are very sensitive to dust, oil and other attached impurities, from performance deterioration caused by the impurities.
In recent years, a demand for a high power laser generator is increased and requirement for a higher energy density of the output light is augmented. However, the optical components are not yet sufficiently protected from being contaminated so achievement of the high power of the laser is obstructed.